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In a recent UK study of 4.1 million selected non-cardiac surgical procedures, a high-risk surgical population which accounted for only 12.5% of in-patient surgical procedures but more than 80% of post-operative deaths was identified.5 This study confirmed the

suspicion that low overall post-operative mortality rates conceal the existence of a large sub-population of patients at much greater risk of post-operative complications and death. Another important finding of this analysis was that fewer than 15% of high-risk surgical patients were admitted to a critical care unit at any time following surgery. The small number of patients who did receive this level of care were discharged after a median of only 24 hours and subsequently lingered for many days on standard surgical wards (median [IQR] stay 16 [10-30] days). However, in this study more detailed analysis of critical care utilisation was not possible because not every critical care unit in the participating centres contributed data to the Intensive Care National Audit & Research Centre (ICNARC) database.

Recent clinical trials suggest that substantial improvements in outcome may be achieved for high-risk surgical patients through the use of protocolised cardio-respiratory therapy delivered in a critical care setting.48,280 However, continued debate over both the size of the high-risk surgical population and the potential benefit of admitting such patients to

critical care represent important obstacles to the introduction of such approaches into routine practice.

This study was designed to examine in more detail the role of critical care in the

management of high-risk surgical patients in the United Kingdom (UK). We used methods similar to those employed in the previous National audit, but conducted the present study in a single institution, so that individual patient data could be cross-referenced using additional local databases and, where necessary, hospital notes. This analysis also

provided an opportunity to confirm or refute the existence of a definable population of high- risk surgical patients within the local surgical population prior to further work investigating the microvascular changes associated with surgery. The aim of this study was to identify patients undergoing selected high-risk non-cardiac surgical procedures within a large NHS Trust and describe critical care resource provision and utilisation for this population in relation to outcome.

3.2 Methods

The study was performed in a large NHS Trust incorporating two teaching hospitals which between them provide all major secondary and tertiary surgical services. This service evaluation was conducted with the approval of the local audit committee. One hospital has 114 surgical beds with a thirteen bed intensive care unit that provides post-operative care for cardiac and other surgical patients as well as medical intensive care for oncology and HIV positive patients. The other hospital has 214 surgical beds with a sixteen bed intensive care unit that provides care for medical, non-cardiac surgical and neurosurgical patients and a six bed high dependency unit providing care for non-cardiac surgical

patients including a large number of patients admitted following traumatic injury. Using an analogous design to the previous national study 5, data was extracted from two databases. The local Hospital Episodes Statistics (HES) database is maintained by clerical coding staff and includes data on all clinical activity within the Trust.281 Validation is performed locally by Trust information managers. The intensive care audit database is maintained locally by dedicated intensive care audit staff and contributes data to the ICNARC case mix programme. These data are subject to local and central internal error checks.282

Data were extracted on all adult (age ≥18 years) surgical admissions to hospital and to critical care between April 1st 2002 and March 31st 2005. All data relating to length of stay were calculated by subtracting the discharge date from the admission date. Surgical specialities with highly developed treatment pathways (often including critical care) such as cardiothoracic surgery and neurosurgery were excluded. Surgical specialities analysed included general and vascular surgery, orthopaedics, gynaecology, ear nose and throat, plastic surgery, urology, maxillofacial and oral surgery. Admissions involving endoscopy, day case surgery, cardio-thoracic surgery, neurosurgery, organ transplantation, obstetrics or the surgical management of burns were excluded. There are 6,920 surgical procedure codes in the Office of Population, Censuses and Surveys (OPCS) classification.283 Surgical admissions to hospital were identified in the HES database by the presence of one of 4,910 codes that satisfied the inclusion criteria. Where more than one surgical procedure was performed during the same hospital admission, only the first procedure was included in the analysis. Several alternative OPCS codes may exist for any given procedure. In order to reduce bias arising from discrepancies in the coding process, procedures were categorised into elective (includes elective and scheduled cases according to ICNARC definition) and non-elective (includes urgent and emergency cases

according to ICNARC definition). Healthcare Resource Groups (HRG) are based on clinical similarity and resource homogeneity.283 The codes may specify the presence of a complicating medical condition, complexity of surgery or a particular age group. HRGs were then ranked according to mortality rates. High-risk surgical procedures were prospectively defined as those procedures included in a HRG with a mortality rate of 5% or more. The remaining procedures were classified as standard risk. Surgical admissions to critical care units were identified in the ICNARC database by source of admission, and were only included if the primary reason for admission was not an excluded surgical procedure. Critical care admissions were prospectively divided into admissions directly from the operating theatre and admissions to critical care following a period of post- operative care on a standard ward. Data describing critical care resource use was verified through a manual check of individual patient details using the ICNARC database.

Data are presented as median [IQR]. Categorical data were tested with Fisher’s exact test and continuous data with the unpaired t test with Welch’s correction. Analysis was performed using GraphPad Prism version 4.0 (GraphPad Software, San Diego, USA). Significance was set at p < 0.05.